Until now, the grid structure and peripheral frame on which individual doors for mail compartments are hung have been made from either a solid metal plate, out of which openings have been cut leaving the appropriate grid structure, or solid extrusions, jointed and held together with fasteners to form the grid structure.
The disadvantages of grid structures made from solid metal plates are large scrap loss and expensive milling while those made of solid extrusions are the absolute requirement of solid extrusions and costly drilling and tapping operations.